Paul Merson says he would be worried about signing Diego Costa after his behaviour at Chelsea but he adds that Atletico Madrid hold all the cards. "I'm a big fan of his football wise - I don't agree with his behaviour now - and on the pitch, he is a top player, but I'd be worried about buying him," he said on The Debate. "When people do this, there is something wrong with you if you're doing something like this. In my wildest dreams, I couldn't do that. I couldn't do it, Mark [Schwarzer, his fellow guest on The Debate] wouldn't do it and I know a lot of footballers who wouldn't. So there has got to be something in his make-up. Why would you buy someone who has got that in them to get up one morning, go home and say 'I'm not coming back'?" While Costa may favour a move to Atletico Madrid, they are currently under a transfer embargo until January 2018 but Merson believes that if a transfer was to happen, the La Liga side would have the power. "Atletico Madrid could be talking to another Spanish club and saying 'we will buy him and you take him on loan for six months for us'," he added. "It seems at the moment, Atletico Madrid are holding all the cards. They don't have to put in a £50m, £40m or £30m bid. They know that he wants to come and could say 'we'll give you £10m to take him off your hands'." Former Blues goalkeeper Schwarzer believes Chelsea are doing the right thing by asking Costa to return and believes that the only person the situation affects is the striker himself. "What they [Chelsea] should do is keep doing what they're doing. They've demanded that he comes back and he isn't. It'll go to FIFA or UEFA and they will try and sort it out through the legal procedures," he told The Debate. "In the meantime, the one person it really affects and is detrimental to is Diego Costa. His career is now at a standstill. Like Merse was saying, if Mr Abramovich decides 'I've had enough, I don't care who he is or how much I'll lost on this deal', although he won't actually because what Costa has done for the club he has made back tenfold already in what he paid in transfer fees.